The University of California San Diego will announce today plans to build a $664 million, 10-story specialty hospital next to its Thornton medical center in La Jolla.

The tower, expected to open by late 2016, marks a major bid by the school to boost its presence in the county’s most lucrative medical market. It will focus on three areas: maternity and infant care, cancer treatment and advanced surgery.

UCSD officials said the expansion, launched with a $75 million donation from Qualcomm founder Irwin Jacobs and his wife, Joan, will enhance research and draw top physicians.

“We want to make UCSD a destination for health care,” said Thomas Jackiewicz, CEO of the nonprofit health system.

But the services envisioned for the Jacobs Medical Center already are provided by four other hospitals in La Jolla and nearby Serra Mesa. It’s unclear whether UCSD can find enough new business — through aging baby boomers, population growth and federal health reform — without having to draw patients away from those competitors.

Maternity care, advanced surgery and cancer treatment will be transferred from the university’s medical campus in Hillcrest to the new tower about 12 miles to the north, reviving criticism that UCSD is retreating from its mission to care for poor and uninsured patients, many of whom live in the southern half of the county.

“It’s completely inconsistent with the commitment they made to this community,” said Chris Van Gorder, president and CEO of Scripps Health, which operates two hospitals in La Jolla, one in Hillcrest and two others in the county. “Part of their responsibility is to keep the hospital system in the county stable, and this isn’t a stabilizing move.”

By shifting some operations to La Jolla, UCSD will increase its access to patients covered by private insurers that generally pay more for hospital services than Medicare, Medi-Cal and the county’s medical programs for the indigent.

The Jacobs Medical Center is part of a larger plan by UCSD to invest about $1 billion to enlarge its medical complex in La Jolla by two-thirds over the next decade. Other projects include the Sulpizio Family Cardiovascular Center, which is scheduled to open in spring 2011; a translational medicine center for turning basic research into health products; and a physician office building.

UCSD leaders have long focused their attention on growth at the Thornton campus.

In 2005, they unveiled a plan to move some inpatient beds and certain services from the Hillcrest hospital to La Jolla. They eventually backed off after receiving heavy criticism from county supervisors, patient advocates and competitors.

The new plan appears to be an attempt to chart a middle course — continuing to serve the county’s poor while pursuing greater market share among middle-class and well-heeled patients.

That strategy has found a backer in the Jacobses, whose gift is the largest-ever donation for a medical cause in the county.

“We are extremely pleased to support this state-of-the-art medical center which will provide both outstanding care for patients, as well as resources for UC San Diego physicians, researchers and their colleagues across the La Jolla mesa to rapidly translate medical research into improved health,” Irwin Jacobs said in a statement.

The Jacobses are among the most prolific philanthropists in the region. Their earlier contributions include $120 million to the San Diego Symphony in 2002 and $110 million for the UCSD Jacobs School of Engineering in 2003.

The couple will join UCSD officials today at the Thornton campus to formally announce details of the new 245-bed hospital. The plan was approved by the UC regents last month. Construction could begin in early 2012 if the project receives preliminary approval from the Office of Statewide Health Planning and Development, Jackiewicz said.

Currently, the university’s medical campus in La Jolla is home to the 119-bed Thornton Hospital, which opened in 1993; the Shiley Eye Center; and the Moores Cancer Center, which houses outpatient services and research activity.

The university’s 386-bed hospital in Hillcrest will keep its trauma center, emergency room, burn center and outpatient services including prenatal care, Jackiewicz said. Most of its rooms will be converted into private, single-patient units, and total bed space will be reduced to 300.

UCSD acquired the Hillcrest center for $17 million in 1980, when it was a county hospital that primarily served the poor.

One potential benefit from converting most of the Hillcrest rooms to private spaces will be a drop in the number of infections that occur during hospital stays, he said.

Devoting the new Jacobs tower to a small number of specialties fits national trends, said Richard Namerow, managing director of the Wellspring Partners hospital consulting firm. Hospitals are gravitating toward services that deliver profitable reimbursements, he said, as well as a burgeoning patient base driven by an older population and legislative changes that will broaden insurance coverage for Americans.

Those factors should produce plenty of patients to fill the new hospital’s rooms and surgical suites, Jackiewicz said.

“If you look at the demographic shifts, everyone is predicting 36,000 more hospital discharges in the county by 2020,” he said. Such growth would require an additional 750 hospital beds.

However, others predict that UCSD will have to grab market share from Scripps and Sharp HealthCare, which operates Sharp Memorial Hospital and Sharp Mary Birch Hospital for Women and Newborns in Serra Mesa.

“It’s not as if these people aren’t already getting this care in La Jolla,” said Nathan Kaufman, a health industry consultant in San Diego.

Dan Gross, an executive for Sharp, said, “I don’t see that (UCSD) is providing new services. … Unquestionably, it does present a change in the status quo. How it will play out is uncertain.”

It’s also uncertain what effect the Jacobs Medical Center might have on the cost of health care in the region.

Increased competition among health systems could give insurers a leg up if they try to negotiate lower reimbursement rates with hospitals, said Gloria Bazzoli, a professor of health administration at Virginia Commonwealth University in Richmond, Va.

But researchers with the Dartmouth Institute for Health Policy and Clinical Practice found that patients use more medical services — and spend more money — when the supply of hospital beds and specialty physicians goes up, without enjoying better health outcomes.

“So you have a potential for a lower price per unit of service (and) potentially an increase in services,” Bazzoli said.